Vivaldi's schtick is that they have every setting and feature that you want and quite a few that you don't. Tab stacks, pinned tabs, split screen, mouse gestures, notes, a full mail client, an RSS reader, ad blocker, custom themes, all built into the browser. And just a ton of customizability. You can control the position and show/hide every UI element (vertical tabs is amazing if you've never tried it), you can create "command chains" (a set of commands which fire in sequence on a keyboard shortcut), and if that's not enough, you can install CSS and JS mods for arbitrary functionality.

But this is just on desktop, just about none of those features exist on mobile right now.